Burner, combustion apparatus, and combustion method

ABSTRACT

A burner includes plural burner ports that produce flames using a first air-fuel mixture and plural auxiliary burner ports that are disposed in a circumference of the burner ports, the plurality of the auxiliary burner ports producing an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture. The air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than 1.

CROSS REFERENCE TO RELATED APPLICATION

This application is entitled to the benefit of priority of Japanese Patent Application No. 2016-150122, filed on Jul. 29, 2016, the contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION i) Field of the Invention

The present invention relates to the combustion technology such as a burner and the like to combust a fuel gas.

ii) Description of the Related Art

There is a burner through which plural thick and thin fuel air-fuel mixtures having air ratios different from each other flow for gas combustion. The air ratio of a thin fuel air-fuel mixture is higher than 1, and the thin fuel air-fuel mixture is an air-rich gas that includes an amount of air more than the amount of air necessary for the complete combustion of the fuel gas. The air ratio of a thick fuel air-fuel mixture is lower than 1, and the thick fuel air-fuel mixture includes an amount of air less than the amount of air necessary for the complete combustion of the fuel gas. As to the combustion of the thin fuel air-fuel mixture, nitrogen oxides (NOx) in the combustion exhaust can be reduced while the stability of the combustion is low. In contrast, as to the combustion of the thick fuel air-fuel mixture, the combustion is highly stable. It is known that, based on the properties of these two, the flame of the thick fuel air-fuel mixture holds the flame of the thin fuel air-fuel mixture to reduce NOx and to enhance the stability of the combustion.

It is known, as to the above gas combustion, that sleeve flames are formed using thick fuel burner ports disposed on both sides of a thin fuel burner port of the burner and the main flame on the side of the thin fuel burner port is held by the sleeve flames (for example, JP 2010-261615A).

BRIEF SUMMARY OF THE INVENTION

As to a burner combusting a fuel gas, the flame of the thick fuel air-fuel mixture having the low air ratio holds the flame of the thin fuel air-fuel mixture having the high air ratio to facilitate reduction of NOx and carbon monoxide (CO) in the combustion exhaust and stabilization of the flame. In this case, the thick fuel air-fuel mixture whose a ratio is high is advantageous to maintain a flame holding performance, while the air-fuel mixture whose the air ratio is low increases the fuel gas unable to be completely combusted due to a shortage of air, and it is therefore difficult to realize reduction of NOx and reduction of CO. A ratio of a thin fuel flame having a high air ratio is advantageously increased to reduce NOx and CO.

When, simply, the ratio of the thin fuel air-fuel mixture is increased and the ratio of the thick fuel air-fuel mixture is reduced, any generation of NOx and CO in the combustion exhaust can be suppressed while the flame holding property is degraded for a lifting that refers to blowing the flame off to occur. A problem therefore arises that the flame becomes unstable.

When the flow velocity of the air-fuel mixture flowing through the burner port on the flame holding side is reduced by reducing the gas amount on the thin fuel air-fuel mixture side, a flashback that refers to combusting the air-fuel mixture in the burner port may occur due to degradation of the balance between the flow velocity of the air-fuel mixture and the combustion velocity of the flame.

In view of the above problems, an object of the present invention is to improve the reduction performance of CO and NOx and to facilitate stabilization of the combustion.

According to an aspect of a burner of the present invention, the burner includes plural burner ports that produce flames using a first air-fuel mixture, and plural auxiliary burner ports that are disposed in a circumference of the burner ports and that produce an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture. The air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than 1.

Other objects, features, and advantages of the present invention will become more apparent by reading the embodiments herein with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram of an example of the configuration of a burner according to an embodiment.

FIG. 2 is a diagram of combustion fields for a main air-fuel mixture f1 and an auxiliary air-fuel mixture f2.

FIG. 3 is a chart of combustion conditions for the burner according to the embodiment. The combustion conditions for the burner are compared to those for a conventional burner.

FIG. 4 is a diagram of an example of the configuration of a combustion apparatus.

FIG. 5 is a diagram of an example of a burner unit.

FIG. 6 is an exploded perspective diagram of the burner unit.

FIG. 7 is an enlarged diagram of a portion of the burner unit.

FIG. 8 is a cross-sectional diagram taken by cutting along a line VIII-VIII of FIG. 7.

FIG. 9 is a cross-sectional diagram taken along a line IX-IX of FIG. 7.

FIG. 10 is a diagram of an example of the state of a main flame F1 and an auxiliary flame F2 in the burner unit portion depicted in FIG. 8.

FIG. 11 is a diagram of an example of the state of the main flame F1 and the auxiliary flame F2 in the burner unit portion depicted in FIG. 9.

FIG. 12 is a diagram of an example of the state of the main flame F1 and the auxiliary flame F2 in the cross-section taken along a line XII-XII of FIG. 7.

FIG. 13 is a diagram of an example of the state of the main flames F1 and the auxiliary flame F2 in the cross-section taken along a line XIII-XIII of FIG. 7.

FIG. 14 is a graph of a result acquired by actually measuring a combustion exhaust gas (for NOx) of the combustion apparatus 20 that includes the burner units 30 and that was loaded on a water heater.

FIG. 15 is a graph of a result acquired by actually measuring a combustion exhaust gas (for CO) of the combustion apparatus 20 that includes the burner units 30 and that was loaded on the water heater.

FIG. 16 is a graph of an example of an experiment on the burner unit.

FIG. 17 is a graph of an example of an experiment on the burner unit.

FIG. 18 is a graph showing a relation of a combustion load, an electric current value of a proportional valve, and a rotation rate of a motor.

FIG. 19 is a diagram of an example of a hardware relating to an air ratio adjustment of the combustion apparatus.

DETAILED DESCRIPTION OF THE INVENTION Embodiment

FIG. 1 depicts an example of the configuration of a burner according to an embodiment. The burner 2 is an example of a burner of this disclosure, and the burner of the invention of this application is not limited to this configuration.

The burner 2 is an example of a what-is-called press burner that is formed from pressed plate members, for example, heat-resistant metal plates, such as stainless steel plates. The burner 2 includes plural burner ports for allowing air-fuel mixtures having different air ratios to flow therethrough, and combusts plural flames having different natures. The burner 2 includes, for example, an air-fuel mixture exhaust part 4 exhausting a main air-fuel mixture f1 that produces main flames, and auxiliary burner ports 6-1 and 6-2 causing an auxiliary air-fuel mixture f2 that produces an auxiliary flame by combustion to flow. The main air-fuel mixture f1 is an example of a first air-fuel mixture of this disclosure and produces the main flames by combustion. The auxiliary air-fuel mixture f2 is an example of a second air-fuel mixture of this disclosure and produces the auxiliary flame by combustion. The air ratio X1 of the main air-fuel mixture f1 has a value higher than 1, and the main air-fuel mixture f1 is in a what-is-called air-rich state. The air ratio X2 of the auxiliary air-fuel mixture f2 is lower than the air ratio X1 of the main air-fuel mixture f1 and has a value higher than 1, and the auxiliary air-fuel mixture f2 is in the what-is-called air-rich state.

The air-fuel mixture exhaust part 4 includes a ribbon 8 formed along the outer shape of the burner 2 that has, for example, a rectangular shape. The ribbon 8 is an example of a rectifying unit that rectifies a flow of the main air-fuel mixture f1. The ribbon 8 has main burner ports 10 that each exhaust and combust the main air-fuel mixture, and squeezed parts 12. The main burner ports 10 and the squeezed parts 12 are alternately formed. The squeezed parts 12 are an example of parts that block any air-fuel mixture from being exhausted, and partition the area of the main burner ports 10 on the ribbon 8 so as to determine the number of the main burner ports 10. For the air-fuel mixture exhaust part 4, the number of the squeezed parts 12 and the size of each of the squeezed parts 12 determine the area of the opening of the main burner ports 10 through which the main air-fuel mixture flows.

The auxiliary burner ports 6-1 and 6-2 open, for example, on both sides of the ribbon 8 along the longitudinal direction of the burner 2. The auxiliary burner ports 6-1 are disposed to be matched with positions of openings of the main burner ports 10, and each exhaust the auxiliary air-fuel mixture f2 on the sides of both edges of the burner 2. The auxiliary burner ports 6-2 are disposed to be matched with positions at which the squeezed parts 12 are formed, and exhaust the auxiliary air-fuel mixture f2 on the inner side of the burner 2 corresponding to the width of the squeezed parts 12. The distance between the auxiliary burner ports 6-2 facing each other over such a squeezed part 12 is shorter than the distance between the auxiliary burner ports 6-1 facing each other over such a main burner port 10. For the burner 2, the flowing-out amount of the main air-fuel mixture f1 is larger compared to that of the auxiliary air-fuel mixture f2 and the flowing-out velocity of the main air-fuel mixture f1 is set to be faster compared to that of the auxiliary air-fuel mixture f2.

The burner 2 has blocking parts 14 each blocking exhausting of any air-fuel mixture. The blocking parts 14 are each formed between the air-fuel mixture exhaust part 4 in which the ribbon 8 is disposed, and the auxiliary burner ports 6-1 and 6-2. The blocking parts 14 are each an insulating region insulating the main burner ports 10 from the auxiliary burner ports 6-1 and 6-2, and form partitioned regions.

<Combustion of Thin Fuel Air-Fuel Mixture f1 and Thick Fuel Air-Fuel Mixture f2>

FIG. 2 depicts combustion fields for the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2. When the states of the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 are shifted into their combustion states by ignition, their combustion fields are formed. On the burner 2, the auxiliary air-fuel mixture f2 exhausted from the auxiliary burner ports 6-1 and 6-2 surrounds the main air-fuel mixture f1 exhausted from the main burner ports 10 in circumference thereof. On the burner 2, centering main flames F1 produced by the combustion of the main air-fuel mixture f1, an auxiliary flame F2 is produced at a low position on the side of the circumferential edge of the main flames F1 and on the side of the burner 2. An independent flame as one of the main flames F1 is produced at each of the main burner ports 10 based on the flow velocity and the combustion of the main air-fuel mixture f1. The main flame F1 with a horizontal cross-section having an oval shape is formed in this example while the horizontal cross-section may have a circular shape.

The pressure of the main air-fuel mixture f1 is lower than that of the auxiliary air-fuel mixture f2 in the blocking part 14. When this pressure relation is set, the auxiliary flame F2 runs into the blocking part 14 to produce the auxiliary flame F2 without independence for each of the auxiliary burner ports 6-1 and 6-2. The auxiliary flame F2 forms a chain-like annular flame surrounding the main flames F1 whose horizontal cross-section has an oval shape. Thereby, each of the main flames F1 is independently formed for each main burner port 10 while the auxiliary flame F2 is present in each interval portion between the main flames F1. Each of the main flames F1 is therefore held in its overall circumference by the auxiliary flame F2 adjacent thereto.

The combustion height of each of the main flames F1 and the auxiliary flame F2 is determined based on, for example, the flow velocity of each of the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2, the combustion velocity corresponding to the fuel gas ratio, and the composition of the fuel gas. For example, the combustion height of the auxiliary flame F2 is set to be lower than that of the main flames F1, so that the auxiliary flame F2 holds the main flames F1 on the side of the foots of the main flames F1, that is, at the portion close to the main burner ports 10. The opening areas of the main burner ports 10 and the auxiliary burner ports 6-1 and 6-2 are set such that the gas flow velocity of the auxiliary air-fuel mixture f2 is lower than the gas flow velocity of the main air-fuel mixture f1.

<Thick Fuel and Thin Fuel Ratio Balance, and Burner Port Shape in Burner Unit 30>

A conventional thick fuel burner port is shaped to hold the thin fuel flame only in the horizontal direction while the auxiliary burner ports 6-2 are each disposed between the main burner ports 10, the auxiliary flame F2 produces pseudo circumferential flames during combustion, and the burner 2 can therefore hold the main flames F1.

Compared to the conventional flame holding in which flames are contacted in parallel faces, in the flame holding conducted by the circular auxiliary flame F2 formed on the burner 2, the contact region for the flames, that is, the area is increased and efficient flame holding can thereby be acquired. This form of the flame holding is pseudo overall-circumferential flame holding and forms an ideal flame holding form that is a form for the circular auxiliary flame F2 to surround the circular main flame F1.

<Setting of Combustion Conditions for Burner 2>

FIG. 3 depicts the combustion conditions for the burner according to the embodiment, being compared to those for the conventional burner. The set conditions depicted in FIG. 3, and the setting approach and the calculation method for the conditions are each an example and the invention of this application is not limited by this configuration.

<Balance of Gas Amount Ratio of Main Air-Fuel Mixture and Auxiliary Air-Fuel Mixture (Auxiliary Air-Fuel Mixture/Main Air-Fuel Mixture Ratio)>

For the burner 2 according to the embodiment, as depicted in FIG. 3, a ratio of the gas amount of the auxiliary air-fuel mixture f2 to the gas amount of the main air-fuel mixture f1 (hereinafter, referred to as a “gas amount ratio”) are set to be, for example, 20:80 or ratios close thereto (for example, 16:84 to 24:76) (“New Burner” in FIG. 3). For a conventional ordinary burner, the gas amount ratio is set to be about 30:70 (“Current” in FIG. 3) for the flame holding capacity of the auxiliary flame and prevention of lifting up of the main flame and the like. This gas amount is the fuel gas amount to be supplied.

The gas amount ratio for an auxiliary thin fuel combustion is determined corresponding to the performance and a purpose of the burner 2. For example, when enhancement is desired for the suppression of the noise value or the prevention of oscillating combustion, a ratio of the gas amount of the auxiliary air-fuel mixture f2 is increased to execute a setting for increasing the load on the side of an auxiliary combustion and, as described later, the ratio of the auxiliary flame F2 is increased that is a stable flame having its air ratio set to be low.

When reduction is desired for the harmful exhaust components such as CO and NOx in the exhaust gas, a setting for increasing a ratio of the gas amount of the main air-fuel mixture f1 is necessary. The air ratio of a main combustion that is the combustion of the main air-fuel mixture f1 is set to be higher as compared to the air ratio of the auxiliary flame that is the combustion of the auxiliary air-fuel mixture f2, the main combustion is combusted in the air-rich state, and generation of any one of these harmful components can therefore be suppressed.

As to the burner 2, due to the configurations of the main burner ports 10 and the auxiliary burner ports 6-1 and 6-2, the auxiliary flame F2 is present in the interval portion between the main flames F1, and the main flames F1 are held on their overall circumferences by the auxiliary flame F2 adjacent to the main flames F1 to thereby enhance the flame holding performance. Any lifting of the main flame, any oscillating combustion, and the like can thereby be prevented even when the gas amount ratio of the auxiliary air-fuel mixture f2 to the main air-fuel mixture f1 is set to be 20:80 or the ratios close thereto for the ultra low NOx regulation.

<Setting of Combustion Air Amount (Air Ratio, and Air/Fuel Ratio (AFR))>

As to the burner 2 according to the embodiment, for example, a combustion air amount of the air-fuel mixture flowing through each of the auxiliary burner ports 6-1 and 6-2 may be set based on the set gas flow amount (the set air-fuel mixture amount) set in advance as a criterion. This set air-fuel mixture amount set in advance is set to be, for example, a value with which no flashback of the flame occurs in the auxiliary burner ports 6-1 and 6-2, based on the combustion velocity corresponding to the components included in the fuel gas, the amount of the air-fuel mixture flowing through the main burner ports 10, and the like. For example, as described, the amount of the air-fuel mixture flowing on the side of the auxiliary burner ports of the conventional burner having the gas amount ratio set to be 30:70 may be used as this set air-fuel mixture amount.

In this embodiment, the case will be described where the amounts of the air-fuel mixtures set for the conventional burner are used as the amount of the air-fuel mixture flowing through each of the auxiliary burner ports 6-1 and 6-2. In this case, An area of the auxiliary burner ports is equal to that of the conventional burner.

The amount of the air-fuel mixture flowing through the conventional auxiliary burner port is represented by “Q_(A1)” and the amount of the air-fuel mixture flowing through the auxiliary burner ports 6-1 and 6-2 is represented by “Q_(A2)”. The conventional air-fuel mixture amount Q_(A1) can be acquired as follows. In this calculation, the case is assumed where methane (CH₄) is the main component.

The air-fuel mixture amount Q _(A1) =A*(1+(Q _(air)*0.8))  (1)

In the equation, “A” represents the supplied fuel gas amount and Q_(air) represents the theoretical air amount to the fuel gas. The case is assumed for Eq. (1) where the air ratios on the main burner ports and the auxiliary burner ports of the conventional burner are set to be 1.6 and 0.8 respectively. With the conventional burner, the air ratio of the air-fuel mixture flowing through the auxiliary burner ports is 1 or smaller. The air-fuel mixture flowing through the auxiliary burner ports is therefore gas-rich, and maintains an oxygen-lacking state.

The burner 2 according to the embodiment is set such that an air-fuel mixture whose an amount is equal to the air-fuel mixture amount Q_(A1) flows through the auxiliary burner ports 6-1 and 6-2.

The air-fuel mixture amount Q _(A2)=(⅔)A*(1+(Q _(air) *X ₁))=Q _(A1)  (2)

When the ratio of the fuel gas amount in the air-fuel mixture is assumed to be small and the fuel gas amount is ignored, the following is acquired.

(⅔)A*(Q _(air) *X ₁)=A*(Q _(air)*0.8)

X ₁=1.25  (3)

In Eq. (2), X₁ is the air ratio on the side of the auxiliary burner ports 6-1 and 6-2 of the burner 2.

For the burner 2 according to the embodiment, the gas amount ratio is changed from 30:70 that is the conventional ratio to 20:80. The ratio of the amount of the fuel gas supplied to the side of the auxiliary burner ports 6-1 and 6-2 is set to be 20 to be reduced compared to that of the conventional burner. Eq. (2) acquires the air ratio X₁ for maintaining the air-fuel mixture amount in the case where the amount A of the gas flowing for the auxiliary flame is set to be ⅔ of the its original amount.

In the case where the amount ratio of the gas flowing on the side of the auxiliary burner ports 6-1 and 6-2 is reduced, when the air ratio equal to the conventional one is maintained, the flow velocity of the air-fuel mixture is reduced and flashback of the flame may occur. Because of this, in the burner 2, the air-fuel mixture is maintained by increasing the air amount corresponding to the reduced amount of the gas flowing on the side of the auxiliary burner ports 6-1 and 6-2. The gas gets the air-rich state in which the air ratio is higher than 1 due to the increase of the air amount in the air-fuel mixture as above. In the burner 2, the flow velocity of the air-fuel mixture can be maintained with the air ratio equal to the conventional air ratio by reducing the burner port area of the auxiliary burner ports 6-1 and 6-2 corresponding to the reduced amount of the gas while the flame holding function may be degraded. When the burner port area of the auxiliary burner ports 6-1 and 6-2 is set to be larger than that of the conventional burner, more air is caused to flow matching with the increased amount of the area while, because the surface area of the burner 2 is limited, the burner port area of the main burner ports 10 is reduced and the flow velocity of the main air-fuel mixture f1 is increased. The burner port areas need to be set in a range where the flame holding performance is not degraded.

For the burner 2, a pilot flame holding state is established for the main flames F1 by the auxiliary burner ports 6-1 and 6-2 even when the air ratio is higher than 1 on the side of the auxiliary flame that hold the main flames, and the flame holding function is thereby secured.

In this case, the main air-fuel mixture amount Q_(B2) may be set related to the main air-fuel mixture amount Q_(B1) of the conventional burner, or the main air-fuel mixture amount Q_(B2) may be set regardless of the main air-fuel mixture amount Q_(B1). The auxiliary air-fuel mixture flow velocity V_(A2) and the main air-fuel mixture flow velocity V_(B2) may be set from, for example, the opening area of the disposed main burner ports 10 or the disposed auxiliary burner ports 6-1 and 6-2, and the supply flow amounts therefor.

<Theoretical Air Amount of Fuel Gas>

The theoretical air amount for the combustion of methane (CH₄) that is a main component of a natural gas and is included in the fuel gas is acquired from a reaction formula below.

CH₄+2O₂+2(79/21)N₂→CO₂+2H₂O+2(79/21)N₂  (4)

In Eq. (4), the second member and the third member on the left-hand side represent the theoretical air amount (Q_(air)) to combust 1 [mol] of methane. In this calculation process, it is assumed that the air contains 79 [%] nitrogen (N₂) and 21 [%] oxygen (O₂). The air necessary for completely combusting 1 [mol] of methane thereby includes 2 [mol] of oxygen and 2*(79/21)=2*3.76 [mol] of nitrogen. The amount of the air including this configuration is acquired from these values using the following equation.

$\begin{matrix} \begin{matrix} {Q_{air} = {{2\; O_{2}} + {2\left( {79/21} \right)N_{2}}}} \\ {= {{2\left( {1 + 3.76} \right)} = {9.52\mspace{14mu}\lbrack{mol}\rbrack}}} \end{matrix} & (5) \end{matrix}$

When Q_(air) of Eq. (2) is substituted by the air amount of Eq. (5),

X₁≈1.2525

is acquired and it can be seen that this value is substantially equal to that of Eq. (3).

The theoretical air amount for propane (C₃H₈) included in the fuel gas will be acquired.

C₃H₈+5O₂+5(79/21)N₂→3CO₂+4H₂O+5(79/21)N₂  (6)

In Eq. (6), the second member and the third member on the left-hand side represent the theoretical air amount (Q_(air)) to combust 1 [mol] of propane. The air necessary for completely combusting 1 [mol] of propane includes 5 [mol] of oxygen and 5*(79/21)=5*3.76 [mol] of nitrogen. The amount of the air including this configuration is acquired from these values using the following equation.

$\begin{matrix} \begin{matrix} {Q_{air} = {{5\; O_{2}} + {5\left( {79/21} \right)N_{2}}}} \\ {= {{5\left( {1 + 3.76} \right)} = {23.8\mspace{14mu}\lbrack{mol}\rbrack}}} \end{matrix} & (7) \end{matrix}$

When Q_(air) of Eq. (2) is substituted by the air amount of Eq. (7),

X₁≈1.221

is acquired and it can be seen that this value is substantially equal to that of Eq. (3).

When the fuel gas (Type 13A) including about 85 [%] methane and about 15 [%] propane is combusted, the air amount is acquired using Eq. (8) below from the calculation results of Eq. (5) and Eq. (7), and the ratios of the constituent elements included in the air for the combustion. To completely combust 1 [mol] of the 13A gas, the air amount is as follows.

0.85*9.52+0.15*23.8=11.7 [mol]  (8)

When Q_(air) of Eq. (2) is substituted by the air amount of Eq. (8),

X₁≈1.2427

is acquired and it can be seen that this value is substantially equal to that of Eq. (3).

For the burner, when the air ratio of the air-fuel mixture is increased, the combustion air amount is increased in proportion to the air ratio. As a result, the flowing-out velocity of the air-fuel mixture is also increased. The degree of stability of the flame is determined based on the balance with the combustion velocity.

Generally, the combustion field is formed at a position that is more distant from the burner port plane on which the flame has a stable state, as the combustion air amount is increased, that is, the air ratio is increased. Because the flame temperature is lowered due to the increase of the air amount, the state of the flame transitions toward its more unstable state. When the air amount is further increased, the lifting of the flame and flameout finally occurs.

Because the burner 2 is a press burner, the air ratio on the side of the main flames F1 is high. The amounts of generated CO and NOx are then increased when the air ratio is reduced to effect stabilization of the main flames F1. The air ratio on the side of the main flames F1 can be set to be high using the flame holding by the auxiliary flame F2.

Because the flame holding function of the auxiliary flame F2 of the burner 2 is high, the main flames F1 are stabilized and generation of CO is suppressed even in the combustion region having a high air ratio.

The air ratio X₁ on the side of the auxiliary burner ports 6-1 and 6-2 is, for example, higher than 1 and equal to or lower than 1.6 to establish the air-rich state. When the air ratio X₁ is 1 and the gas amount ratio is changed from the conventional ratio of 30:70 to Z1:(100−Z1), Eq. (2) is as follows.

The air-fuel mixture amount Q _(A2)=(Z1/30)A*(1+(Q _(air)*1))=Q _(A1)   (9)

When the ratio of the fuel gas amount in the air-fuel mixture is assumed to be small and the fuel gas amount is ignored, the following is acquired.

A*(Q _(air)*0.8)=(Z1/30)A*(Q _(air)*1)

Z1=24  (10)

When the air ratio X₁ is 1.6 and the gas amount ratio is changed from the conventional ratio of 30:70 to Z2:(100−Z2), Eq. (2) is as follows.

The air-fuel mixture amount Q _(A2)=(Z2/30)A*(1+(Q _(air)*1.6)=Q _(A1)   (11)

When the ratio of the fuel gas amount in the air-fuel mixture is assumed to be small and the fuel gas amount is ignored, the following is acquired.

A*(Q _(air)*0=(Z2/30)A*(Q _(air)*1.6)

Z2=15  (12)

The gas amount ratio is consequently set to be, for example, 15:85 to 24:76.

Eq. (10) and Eq. (12) show that the air ratio of the auxiliary air-fuel mixture f2 is increased when the ratio of the gas in the auxiliary air-fuel mixture f2 is reduced. On the other hand, the air ratio of the main air-fuel mixture f1 is reduced. Preferably, the air ratio of the main air-fuel mixture f1 is equal to or higher than the air ratio of the auxiliary air-fuel mixture f2.

The gas amount ratio of Z3:(100−Z3) will be acquired with which the air ratio of the main air-fuel mixture f1 and the air ratio of the auxiliary air-fuel mixture f2 are both X₃. When the air ratio of the auxiliary air-fuel mixture f2 is X₃ and the gas amount ratio is changed from the conventional ratio of 30:70 to Z3:(100−Z3), Eq. (2) is as follows.

The air-fuel mixture amount Q _(A2)=(Z3/30)A*(1+(Q _(air) *X ₃))=Q _(A1)   (13)

When the ratio of the fuel gas amount in the air-fuel mixture is assumed to be small and the fuel gas amount is ignored, the following is acquired.

A*(Q _(air)*0.8)=(Z3/30)A*(Q _(air) *X ₃)  (14)

Similarly, at the air ratio X₃, the main air-fuel mixture f1 has the air ratio of 1.6 for the new gas amount ratio of 20:80, and the following is therefore acquired.

B*(Q _(air)*1.6)=((100−Z3)/80)B*(Q _(air) *X ₃)  (15)

“B” in the equation is the fuel gas amount to be supplied. From Eq. (14) and Eq. (15), Z3 is 15.79. Preferably, the gas amount ratio is set to be 16:84 to 24:76.

<Combustion Velocity>

The combustion velocity of each of hydrocarbons represented by methane is closely related to the air ratio. The combustion velocity becomes maximal in the vicinity of the air ratio of 1 and is reduced therefrom before and after this air ratio. This is because a formation position of the combustion field becomes distant from the burner port plane on which the combustion is stable, and the flame therefore becomes unstable. Because the combustion velocity is reduced as the air ratio is increased, stable flame holding by a thick fuel air-fuel mixture is indispensable for the thin fuel flame F1.

For example, a value close to a set value may arbitrary be set as the air-fuel mixture amount of the burner 2. In this case, for the burner 2, the auxiliary air-fuel mixture flow amount X₁₋₁ and the main air-fuel mixture flow amount X₂₋₁ may arbitrary be set at ratios within the predetermined range based on, for example, the set flow amount.

<Combustion Apparatus>

FIG. 4 depicts an example of the configuration of a combustion apparatus. The combustion apparatus 20 is an example of a combustion apparatus of the present invention.

The combustion apparatus 20 is used as a heat source apparatus for a water heater or a heating water heater that uses a fuel gas or the like as fuel. The combustion apparatus 20 has a combustion chamber 24 disposed in an apparatus housing 22. The combustion chamber 24 is surrounded by a side wall part 26 of the apparatus housing 22. A burner 28 that combusts a fuel gas is installed in the combustion chamber 24. The burner 28 is an example of the burner of this disclosure and includes plural burner units 30 combined with each other, and forms a uniform burner port plane as an example.

A supporting part 32 protruding toward the side of the circumference of the combustion chamber 24 is disposed in the upper portion of the side wall part 26. A heat exchanger not depicted is disposed on the upper face of the supporting part 32, and the combustion exhaust of the burner 28 is caused to flow through the heat exchanger. The heat of the combustion exhaust acquired from the combustion of the fuel gas is heat-exchanged by the heat exchanger.

Plural first fuel supply ports 34-1 and second fuel supply ports 34-2 are formed in the side wall part 26 of the apparatus housing 22. The fuel supply ports 34-1 are openings to supply the fuel gas to the side of the main burner ports of the burner unit 30. The fuel supply ports 34-2 are openings to supply the fuel gas to the side of the auxiliary burner ports of the burner unit 30.

On the outer side of the fuel supply ports 34-1 and 34-2, a fuel supply unit 36 is disposed that is common to the fuel supply ports 34-1 and 34-2. The fuel supply unit 36 includes plural first fuel injection nozzles 38-1 and second fuel injection nozzles 38-2. The fuel injection nozzles 38-1 are disposed on the side of the fuel supply ports 34-1 and the fuel injection nozzles 38-2 are disposed on the side of the fuel supply ports 34-2. The fuel gas is thereby supplied to the inside of the burner unit 30. In this example, the fuel supply ports 34-1 each have, for example, an oval shape and the fuel supply ports 34-2 each have, for example, a circular shape. The fuel injection nozzles 38-1 and the fuel supply ports 34-1 are used to supply the main air-fuel mixture f1 to the main burner ports 10, and the fuel injection nozzles 38-2 and the fuel supply ports 34-2 are used to supply the auxiliary air-fuel mixture f2 to the auxiliary burner ports 6-1 and 6-2. The opening area of a fuel supply port 34-1 is larger than that of a fuel supply port 34-2 and these opening areas cause the introduction amount of the air to differ for the supply of the fuel gas to differ the air ratio of the main air-fuel mixture produced on the side of the fuel supply port 34-1 from the air ratio of the auxiliary air-fuel mixture produced on the side of the fuel supply port 34-2.

Adjustment of the gas amount ratio of the auxiliary air-fuel mixture f2 to the main air-fuel mixture f1 is conducted by, for example, adjustment of the ratio of the opening area of the fuel injection nozzle 38-2 to the opening area of the fuel injection nozzle 38-1. To set this gas amount ratio to be, for example, 20:80, the ratio of the opening area of the fuel injection nozzle 38-2 to the opening area of the fuel injection nozzle 38-1 is adjusted to be, for example, 20:80. The opening areas of the fuel supply ports 34-1 and 34-2 are adjusted to acquire the aimed air ratio using, for example, the opening areas of the fuel injection nozzles 38-1 and 38-2 as criteria. The opening areas of the fuel supply ports 34-1 and 34-2 may be adjusted by adjusting the diameters of the openings in view of a difference in the air ratio of the auxiliary air-fuel mixture f2 to the main air-fuel mixture f1 and a difference in the degree of flowability between the air-fuel mixtures, the opening areas may be adjusted by blocking a portion of the openings with a blocking member such as a blocking plate, or the ratio of the opening areas may be different from the ratio of the opening areas of the fuel injection nozzles 38-1 and 38-2.

The side wall part 26 on the side of the fuel supply ports 34-1 and 34-2 dents toward the inside of the apparatus housing 22, and the apparatus housing 22 has a fuel supply chamber 39 formed in the apparatus housing 22. The fuel supply chamber 39 is an example of a means of accumulating therein the fuel gas and supplying the fuel gas to the fuel supply ports 34-1 and 34-2, and constitutes the fuel supply unit 36.

The apparatus housing 22 is closed on the side of its bottom face by a bottom face plate 40. The bottom face plate 40 has an air inlet 42 formed therein. An air supply fan 44 is disposed on the side of the lower face of the bottom face plate 40 and the air supply fan 44 is connected to the air inlet 42. The air supply fan 44 includes a motor 46, and the rotation of the motor 46 supplies the combustion air from the air supply fan 44 to the air inlet 42. The combustion air is introduced into the burner unit 30 in response to the injection of the fuel gas and is used for the combustion of the fuel gas.

<Burner Unit 30>

FIG. 5 depicts an example of the burner unit. The burner unit 30 is an example of the burner of the present invention.

The burner unit 30 is a what-is-called press burner that is formed by plate members acquired by pressed heat resistant metal plates such as stainless steel plates. Each burner unit 30 includes independent mixing units 48-1 and 48-2. In the mixing unit 48-1, the fuel gas supplied from the fuel injection nozzle 38-1 and the combustion air are mixed with each other to produce the main air-fuel mixture. In the mixing unit 48-2, the fuel gas supplied from the fuel injection nozzle 38-2 and the combustion air are mixed with each other to produce the auxiliary air-fuel mixture. The burner unit 30 includes a main body part 50, a rectifying part 52, and a burner port part 54 in this order from the lower side toward the side of the burner ports, and these parts are integrally formed by the plate members.

In the main body part 50, air-fuel mixture entrance ports 56-1 and 56-2 are disposed and formed at two vertical levels. The air-fuel mixture entrance port 56-1 is an opening that has a flat hexagonal shape or that is a long hole and is connected to the fuel supply port 34-1 for the main air-fuel mixture f1 to be introduced. The air-fuel mixture entrance port 56-2 is an opening that has a circular shape and is connected to the fuel supply port 34-2 for the auxiliary air-fuel mixture f2 to be introduced.

The rectifying part 52 rectifies the flow of the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 that are introduced into the main body part 50 to introduce the air-fuel mixtures f1 and f2 into the burner port part 54. The rectifying part 52 has the ribbon 8 disposed in the air-fuel mixture exhaust part 4. The ribbon 8 is disposed in the air-fuel mixture exhaust part 4 of the burner unit 30, and is detachable.

For example, as depicted in FIG. 6, the burner unit 30 is formed by joining inner wall plates 60 and outer wall plates 62 on the right and the left sides of the ribbon 8. The inner wall plates 60 and the outer wall plates 62 are formed out of common metal plates. The ribbon 8 is sandwiched between the inner wall plates 60 facing each other, the inner wall plates 60 are joined with each other, and a mixing unit 48-1 and the air-fuel mixture exhaust part 4 that exhausts the produced main air-fuel mixture are thereby formed in the joining portion. As to the joined outer wall plates 62, the mixing unit 48-2 and the auxiliary burner ports 6-1 and 6-2 are formed between the outer wall plates 62 and the inner wall plates 60.

The burner port part 54 is formed on the upper face of the burner unit 30, includes the plural main burner ports 10 formed by the ribbon 8 at constant intervals, and includes the plural first and the second auxiliary burner ports 6-1 and 6-2 regularly at constant intervals on the side of the main body part 50. In the air-fuel mixture exhaust part 4 of this example, 12 main burner ports 10 are formed and arranged in a row by at least one ribbon 8. In the combustion apparatus 20, due to the plural burner units 30 disposed in parallel to each other, the main burner ports 10 are arranged in plural rows and plural columns to form the burner port part 54 forming a uniform face portion. The ribbon 8 may be divided into plural pieces and be disposed in the air-fuel mixture exhaust part 4.

In the burner unit 30 except the air-fuel mixture entrance ports 56-1 and 56-2, and the burner port part 54, an edge portion 58 is formed by adhering plate members to each other. This edge portion 58 reinforces the burner unit 30.

FIG. 7 depicts an enlarged view of a portion of the burner unit.

The ribbon 8 is formed by, for example, press working from metal plates such as stainless steel and includes 6 metal plates in this embodiment. The ribbon 8 has the main burner ports 10 and the squeezed parts 12 alternately disposed therein. Each of the main burner ports 10 has 5 long burner ports 64 formed therein. The long burner ports 64 are lined in a direction perpendicular to the arrangement direction of the main burner ports 10 and are formed from, for example, 6 metal plates whose bending angles differ from each other. The shape of each of the long burner ports 64 is symmetric in the right-and-left direction with respect to a center line taken in the longitudinal direction of the ribbon 8. The flow of the main air-fuel mixture f1 is rectified due to the formation of the plural long burner ports 64 to form parallel flows, and the main air-fuel mixture f1 flows out from the main burner ports 10.

The width in the longitudinal direction of each auxiliary burner port 6-1 is smaller than the width of each long burner port 64 of the main burner port 10, and the opening area of each auxiliary burner port 6-1 is smaller than the opening area of one long burner port 64. The flowing-out velocity of the auxiliary air-fuel mixture f2 flowing out from the auxiliary burner ports 6-1 can thereby be set to be faster than the combustion velocity of the auxiliary air-fuel mixture f2.

The auxiliary burner ports 6-1 and 6-2 are formed by joining the inner wall plates 60 and the corresponding outer wall plates 62 with each other. The inner wall plates 60 and the outer wall plates 62 are common thereto. For example, the inner wall plates 60 are bent in a trapezoidal shape to protrude bending parts toward the side of the squeezed parts 12, and the outer wall plates 62 are similarly bent into the auxiliary burner ports 6-2 to protrude bending parts 66. Thereby, each auxiliary burner port 6-2 has a substantially trapezoidal opening shape and each bending part 66 of the outer wall plates 62 makes an opening area of one of the auxiliary burner ports 6-2 small. The auxiliary burner port 6-2 formed and disposed as above has the opening area larger than that of the auxiliary burner port 6-1 and has the flowing-out amount of the auxiliary air-fuel mixture f2 larger than that of an auxiliary burner port 6-1. Furthermore, each auxiliary burner port 6-2 projects into the blocking part 14 to be close to the squeezed part 12. Thereby, coupling of the auxiliary flame F2 (FIG. 2) is facilitated by the auxiliary air-fuel mixture f2 flowing out from a pair of the auxiliary burner ports 6-2. As to the ratio of the areas of the auxiliary burner ports 6-1 and 6-2, the former may be greater than the latter or the latter may be greater than the former.

FIG. 8 depicts a cross-section taken by cutting along a line VIII-VIII of FIG. 7. A pair of the blocking parts 14 are formed in the burner port part 54 of the burner unit 30, sandwiching the main burner ports 10 formed by the ribbon 8, and the auxiliary burner ports 6-1 are formed on the outer side of the blocking parts 14. The opening edge portions of the inner wall plates 60 of the auxiliary burner ports 6-1 are disposed in the same plane as that of the main burner ports 10. In contrast, the outer wall plates 62 are set to be higher than, for example, the inner wall plates 60 by a height of h1. The burner port part 54 is thereby surrounded by the opening edge portions of the high outer wall plates 62.

The blocking parts 14 are formed by causing protrusions 68 protruding from the middle portion of the inner wall plates 60 toward the side of the ribbon 8 to abut the ribbon 8.

The auxiliary air-fuel mixture f2 is guided from the side of the main body part 50 to each auxiliary burner port 6-1 through auxiliary air-fuel mixture supply paths 70.

FIG. 9 depicts a cross-section taken along a line IX-IX of FIG. 7. In the burner unit 30, a pair of the blocking parts 14 are formed, sandwiching the squeezed parts 12 of the ribbon 8 and a pair of the auxiliary burner ports 6-2 are formed on the outer side of the blocking parts 14.

In the middle portion of the ribbon 8, protrusions 69 are formed by bending metal plates outward. The protrusions 69 abut the inner wall plates 60. The halfway portions of the inner wall plates 60 project toward the side of the squeezed parts 12 of the ribbon 8. The interval between the auxiliary burner ports 6-2 facing each other is thereby reduced. The opening area of each of the auxiliary burner ports 6-2 is reduce by the bending parts 72 of the outer wall plates 62. The auxiliary burner ports 6-2 are also surrounded by the outer wall plates 62 that are higher by a height h1.

<Combustion of Main Air-Fuel Mixture f1 and Auxiliary Air-Fuel Mixture f2>

When the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 transition into their combustion state due to ignition, combustion fields are formed. With the main air-fuel mixture f1, the independent main flames F1 are produced at each main burner ports 10 based on the flow velocity and the combustion of the main air-fuel mixture f1. Compared to the auxiliary air-fuel mixture f2, the main air-fuel mixture f1 has a larger flowing-out amount and has a higher flowing-out velocity. The main air-fuel mixture f1 flowing out from the main burner ports 10 is surrounded by the auxiliary air-fuel mixture f2 flowing out from the plural auxiliary burner ports 6-1 and 6-2. The shape of the main flame F1 is, for example, an oval shape, a circular shape, or the like in its horizontal cross-section.

FIG. 10 depicts an example of the state of the main flame F1 and the auxiliary flame F2 in the burner unit portion depicted in FIG. 8. The pair of parts of auxiliary flame F2 are formed, sandwiching the main flame F1. In this case, the auxiliary air-fuel mixture f2 has a pressure that is higher than that of the main air-fuel mixture f1 in the blocking parts 14 between the auxiliary air-fuel mixture f2 and the main flames F1. The auxiliary air-fuel mixture f2 thereby runs into the blocking parts 14. In the auxiliary flame F2, a flow velocity of the air-fuel mixture is lower than that in the main flames F1 and the burner port area is smaller than that therein, and the auxiliary flame F2 therefore is smaller than the main flames F1. The auxiliary flame F2 thereby combusts in the vicinity of the burner port part 54 in contrast with the main flames F1 whose flame length is large and that combust at a position away from the burner port part 54. The auxiliary flame F2 combusts in the vicinity of the foots of the main flames F1 to surround the main flames F1. Even with the flames in the what-is-called air-rich state in which the air ratio of the air-fuel mixture is higher than 1, the pilot flame holding state is established and the auxiliary flame F2 holds the main flames F1 to block any being blown-off of the flames, by forming the above combustion state.

FIG. 11 depicts an example of the state of the main flame F1 and the auxiliary flame F2 in the burner unit portion depicted in FIG. 9. The auxiliary flame F2 is formed in the interval portion between the main flames F1. The flame length of the auxiliary flame F2 stretches on the portion of each auxiliary burner port 6-2 and the auxiliary flame F2 becomes higher thereon. The pressure in the blocking parts 14 adjacent to auxiliary flame F2 is lower than that of the auxiliary air-fuel mixture f2 and, as above, the auxiliary flame F2 produced by the auxiliary air-fuel mixture f2 runs into the blocking parts 14 and the occluding squeezed part 12. The outer wall plates 62 surround the auxiliary flame F2 formed at each auxiliary burner port 6-2 for unifying the auxiliary flame F2 to be facilitated. The circumferences of the main flames F1 are thereby surrounded by the auxiliary flame F2 without any interval in a circled state for the main flames F1 to be held.

FIG. 12 depicts an example of the state of the main flame F1 and the auxiliary flame F2 taken in a XII-XII portion of FIG. 7. For one main flame F1, auxiliary flame F2 is formed by the plural auxiliary burner ports 6-1 and 6-2. A pressure in the blocking part 14 between the auxiliary burner ports 6-1 and 6-2 is lower than that of the auxiliary air-fuel mixture f2, and the auxiliary flame F2 run into the side of the blocking part 14. The auxiliary flame F2 running thereinto combusts in the vicinity of the squeezed parts 12 and in the vicinity of the long burner ports 64. Because the flame length of the auxiliary flame F2 stretches in the portions of the auxiliary burner ports 6-1 and 6-2, a wavy flame shape with unevenness is produced.

FIG. 13 depicts an example of the state of the main flames F1 and the auxiliary flame F2 in the cross-section taken along a line XIII-XIII of FIG. 7. The main flames F1 are each independently formed. While the auxiliary flame F2 is present in the interval portion between the main flames F1, and each main flame F1 is therefore held on its overall circumference by the auxiliary flame F2 adjacent to each main flame F1.

<Effects and Characteristic Features of the Embodiment>

(1) Combustion Function

The auxiliary burner ports 6-1 and 6-2 produce the auxiliary flame F2 and thereby hold the main flames F1. The auxiliary flame F2 is a stable flame and is used within a range where CO and NOx amounts are permitted under a predetermined standard. The main burner ports 10 produce the main flames F1 to be the main heat source. The main flames F1 are unstable flames and the flame holding by the auxiliary combustion at the auxiliary burner ports 6-1 and 6-2 is indispensable therefor.

(2) Used Air Ratio

The used air ratio of the auxiliary air-fuel mixture f2 flowing into the side of the auxiliary burner ports 6-1 and 6-2 is set to be a value higher than 1 for the auxiliary air-fuel mixture f2 to set an air-excessive state. The region of the used air ratio of the main air-fuel mixture f1 flowing into the side of the main burner ports 10 is set to be 1.6 or about 1.6 for the main air-fuel mixture f1 to be set an air-excessive state. The air ratios of the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 differ from each other and are set so that the air ratio of the main air-fuel mixture f1 is higher than the air ratio of the auxiliary air-fuel mixture f2.

(3) Degree of Stability of Flame

As to the combustion at each of the auxiliary burner ports 6-1 and 6-2, the air ratio is higher than 1 while stable flames are acquired by adjusting the flow velocity of the air-fuel mixture. As to the combustion flames at the main burner ports 10, the air is excessive, the belching velocity is higher than the combustion velocity, and the flame temperature is low. This flame therefore tends to suffer the lifting.

(4) Flame Form

As to the auxiliary combustion at each of the auxiliary burner ports 6-1 and 6-2, the belching velocity is close to the combustion velocity, the auxiliary flame F2 has a short flame length and is small. As to the main combustion at the main burner ports 10, the belching velocity is high and the combustion in a high air ratio is established (with a low combustion velocity). Due to this, the main combustion has a long flame length to produce a large flame.

(5) Generation of CO

The generation of CO can be reduced in the main combustion at the main burner ports 10, and the generation of CO can be suppressed by setting the auxiliary air-fuel mixture f2 flowing to the auxiliary burner ports 6-1 and 6-2 to be air-excessive.

(6) Generation of NOx

The generation of NOx can be reduced by setting both of the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 to be air-excessive.

(7) Lifting and Flashback

As to the auxiliary air-fuel mixture f2 flowing to the auxiliary burner ports 6-1 and 6-2, for the reduced gas amount, the burner port areas of the auxiliary burner ports 6-1 and 6-2 are each set to be equal to or larger than the burner port area of the auxiliary burner port of the conventional burner and more air is caused to flow. No flashback of the flame thereby tends to occur. The auxiliary flame F2 holds the main flames F1 on their overall circumference, and the flame holding function is thereby enhanced and no lifting of the main flames F1 tends to occur. In a thick and thin fuel horizontal arrangement of a conventional burner in which a thin fuel flame positioned on the side of a thick fuel flame is held by the thick fuel flame, the thin fuel flame does not leave the vicinity of the burner port and a stable flame is formed. However, a thin fuel flame away from the side of the thick fuel flame is held by only the thin fuel flames and the length of the thin fuel flame is large. The lifting therefore tends to occur and excessive CO tends to be generated. When the air ratio is high or when the thick fuel/the thin fuel ratio is extremely low, these tendencies are conspicuous. Due to this, the usable combustion region (the air ratio and the combustion load) is limited for this combustion. In contrast, the pseudo overall-circumferential flame holding is established on the burner unit 30 according to the embodiment and the above inconvenience is therefore not present.

(8) From the Above, According to the Burner Unit 30 of this Embodiment, the Following Effects can be Acquired.

a) The flame holding function of the auxiliary flame for the main flame can be enhanced, stabilization of the combustion of the main flame can be facilitated, and reduction of CO and NOx can be facilitated by the combustion of the main flames and the auxiliary flame.

b) The range of the usable air ratio is extended and the air ratio can be reduced due to the reduction of CO and NOx, and the stabilization of the combustion. The air supply capacity of the air supply fan can therefore be suppressed.

c) The controllability of the combustion can be enhanced, and downsizing of the burner and an increase of the output thereof can be facilitated.

<Thick Fuel/Thin Fuel Ratio Balance (Taking Air Ratio into Consideration)>

Items to be controlled of each of the auxiliary burner ports 6-1 and 6-2 include the burner port shape, the burner port area, the gas amount ratio, and the like. The air ratios of the auxiliary flame F2 and the main flame F1 need to be taken into consideration to determine the gas amount ratio thereof. For example, when the air ratio on the auxiliary burner ports 6-1 and 6-2 is set to be higher than 1, the combustion of the auxiliary flame F2 is close to that of the main flames F1. This auxiliary flame F2 reduces exhaust of CO and NOx (NOx can be reduced with the air ratio equal to or higher than 1.2) but causes an increase of the belching velocity of the auxiliary air-fuel mixture f2 constituting the auxiliary flame F2 and reduction of the flame temperature, and the tendency for the lifting may be enhanced. Taking into consideration this point of view, the burner unit 30 according to the embodiment realizes production of the auxiliary flame F2 with concurrently suppressed exhausts of CO and NOx by establishing the gas amount ratio balance and reducing the flow amount of the air-fuel mixture flowing through the auxiliary burner port.

As to the auxiliary burner ports 6-1 and 6-2, the air ratio of the auxiliary flame F2 is set to be a value close to that of the main flames F1 because the overall-circumference flame holding is conducted for the main flames F1 using the auxiliary flame F2. The flame holding function is therefore enhanced even when the air ratio of the auxiliary flame F2 is increased and the auxiliary flame F2 tends to have the lifting. As a result, CO and NOx mainly generated in the auxiliary flame F2 can be reduced. When the air ratio of the auxiliary flame F2 is set to be around the theoretical value of A=1, the thermal NOx becomes conspicuous and the production velocity of the thermal NOx is therefore reduced. In this case, the flame temperature is set to be, for example, lower than 1,800° C. and the air ratio is set to be equal to or higher than 1.2.

<Thick Fuel/Thin Fuel Ratio Balance>

The gas amount ratio of the air-fuel mixture is determined corresponding to the performance and the purpose of the burner unit 30. For example, when the suppression of the noise value and the prevention of the oscillating combustion are enhanced, a setting is made for the gas amount ratio to be increased, that is, an increase of the load on the side of the auxiliary combustion, and the rate of the auxiliary flame F2 to be the stable flame is thereby increased. When reduction of the harmful exhaust components, such as CO and NOx is desired in the exhaust gas, a setting is necessary to reduce the air ratio of the auxiliary air-fuel mixture f2. Compared to the auxiliary combustion to be the combustion of the auxiliary air-fuel mixture f2, the thin fuel combustion to be the combustion of the main air-fuel mixture f1 combusts on the side of an excessive air ratio and any generation of these harmful components is therefore suppressed.

<Results of Experiments>

(1) Relation Between Air/Fuel Ratio and Combustion Exhaust Gas

FIGS. 14 and 15 depict results acquired by actually measuring a combustion exhaust gas (for NOx and CO) when the combustion apparatus 20 including the burner units 30 was loaded into a water heater. “A” represents the result of an experiment for the combustion apparatus 20 that is an example of the combustion apparatus of the present invention, and “B” represents the result of measurement using the conventional burner as Comparative Example. The thick fuel/thin fuel ratio was 20:80 and the input was 58.1 [kW].

As depicted in FIG. 14, as to the relation between the air/fuel ratio and NOx, the line of the reference value represents the NOx regulation value of California in the U.S. that is an internationally very strict exhaust standard. With the conventional burner, when the air/fuel ratio is set to be high, the “B” is able to be reached to the standard while an NOx exhaust amount lower than the reference value is able to be realized within a wide range of air/fuel ratio when the burner unit 30 is used. Although FIG. 14 depicts the relation between the air/fuel ratio and NOx, a relation between the air ratio and NOx has the same tendency as or similar tendency to the relation between the air/fuel ratio and NOx. That is, with the conventional burner, when the air ratio is set to be high, the “B” is able to be reached to the standard while the NOx exhaust amount lower than the reference value is able to be realized within a wide range of the air ratio when the burner unit 30 is used.

As depicted in FIG. 15, as to the relation between the air/fuel ratio and CO [%], the line of the reference value represents the regulation value of ANSI 221.10.3, the North American water heaters standard, that is an internationally very strict exhaust standard. Similarly to the result for NOx, it can be seen that the CO exhaust amount is equal to or smaller than the reference value within a wide range of air/fuel ratio for a burner unit 12. Although FIG. 15 depicts the relation between the air/fuel ratio and CO [%], a relation between the air ratio and CO [%] has the same tendency as or similar tendency to the relation between the air/fuel ratio and CO [%]. That is, it can be seen that the CO exhaust amount is equal to or smaller than the reference value within a wide range of the air ratio for a burner unit 12. CO exhaust amount does not become equal to or smaller than the reference value with the conventional burner.

A value in the vicinity of “C” is used as the best air/fuel ratio for the conventional burner while the air/fuel ratio and the air ratio is reduced as a first means for the described burner unit 30. When the flowing-out velocity of the main air-fuel mixture f1 is increased, the generation ratio of CO is also increased while, as is apparent from the graph of FIG. 15, CO [%] maintains a certain low value even when the flowing-out velocity of the main air-fuel mixture f1 is increased, that is, the combustion velocity is increased when the air/fuel ratio and the air ratio are increased. The flowing-out velocity of the main air-fuel mixture f1 is therefore increased as a second means. Working a combination of the first and the second means or either one thereof can reduce exhaust of CO, NOx, and the like, maintaining or increasing the heat amount per unit area of the burner port part 54.

(2) State of Air Ratio and Combustion State for Air-Fuel Mixture Flow Velocity of Burner Unit 30 to be One Example of Invention of this Application

As depicted in FIG. 16, the burner unit 30 can flow out the air-fuel mixtures for the air-fuel mixtures to each have a set air ratio in the main burner ports 10 and the auxiliary burner ports 6-1 and 6-2. Of these, for the auxiliary burner ports 6-1 and 6-2, the air ratios were measured for the auxiliary flame being disposed on the right side and left side of the main burner ports of the burner unit 30 as a center as one set. According to the measurement, for the burner 2, the air ratio of the main flame is 1.66 in average with a certain amount of error, and the air ratio of the auxiliary flame is 1.22 in average for not only the right one but also the left one with a certain amount of error.

For the combustion apparatus 20 including the burner unit 30, for example, as depicted in FIG. 17, the air-fuel mixture flow velocity was measured for each predetermined combustion load (Input). According to the measurement, for the burner unit 30 and the conventional burner, the ranges of the air-fuel mixture flow velocity of the auxiliary flame against the combustion load overlap with each other. The burner unit 30 with a reduced gas amount ratio thereby exhibits the combustion state similar to that of the burner combusting the conventional thick fuel and thin fuel air-fuel mixtures. With the burner unit 30, no flashback of any flame occurs at the auxiliary burner ports 6-1 and 6-2 by maintaining the air-fuel mixture flow velocity against the combustion load.

OTHER EMBODIMENTS

(1) It is described in the above embodiment that the air ratio of the auxiliary air-fuel mixture flowing through the burner 2 and the amounts of the air-fuel mixtures are calculated using the values set in advance or the amounts of the air-fuel mixtures of the conventional burner while the calculation is not limited to this. The air ratio of the auxiliary air-fuel mixture and the amounts of the air-fuel mixtures may be set based on, for example, the calculation of the air-fuel mixture flow velocity V_(A1) and V_(A2). For the burner 2, the air-fuel mixture amount Q_(A2) may be set such that, for example, the air-fuel mixture flow velocity V_(A2) is equal to the flow velocity V_(A1) of the air-fuel mixture exhausted from the auxiliary burner port of the conventional burner.

(2) In addition, for the burner 2, after the values of the gas amount ratio is set, the air ratio X₂₋₂ of the auxiliary air-fuel mixture f2 and the auxiliary air-fuel mixture amount Q_(A3) may be able to be arbitrarily set within predetermined condition ranges.

(3) It is described in the above embodiment that the auxiliary burner port 6-1 is formed by one single opening while the auxiliary burner port 6-1 is not limited to this and the auxiliary burner port 6-1 may be formed by plural openings lining with the main burner port 10.

(4) The auxiliary burner ports 6-2 may be arranged so that their protruding tips abut on the side of the squeezed part 12 of the ribbon 8. The auxiliary flame F2 sandwiching the squeezed parts 12 can thereby be closely cohered and the flame holding function for the main flames F1 can be enhanced.

(5) In the above embodiment, the hole shape of the main burner ports 10 is set to be the flat hexagonal shape while the hole shape may be set to be an oval shape or a circular shape.

(6) In the above embodiment, the hole shape of the auxiliary burner ports 6-1 is set to be the flat rectangular shape while the hole shape may be set to be an oval shape or a circular shape.

(7) In the above embodiment, the hole shape of the auxiliary burner ports 6-2 is set to be the trapezoidal shape while the hole shape may be set to be an oval shape or a circular shape.

(8) A third auxiliary burner port may be formed in the blocking part 14 located between the auxiliary burner ports 6-2 of the above embodiment to hold the main flame.

(9) It is described in the above embodiment that the air ratios of the air-fuel mixtures are set to be specific values for the air-fuel mixtures to combust while the air ratios are not limited to this. For the combustion apparatus 20, the air ratios may be adjusted corresponding to, for example, the combustion amount of the burner unit 30. The combustion apparatus 20 controls a rotation rate of the motor 46 of the air supply fan 44 and the supply amounts of the fuel gas, for example, to adjust the air ratios of the air-fuel mixtures. In this case, the main air-fuel mixture f1 and the auxiliary air-fuel mixture f2 each have the air ratio higher than 1.

The air ratios of the air-fuel mixtures are adjusted based on, for example, an electric current value of a proportional valve for gas against the combustion load indicated by a solid line in FIG. 18 and the rotation rate of the motor 46 of the air supply fan 44 against the electric current value of the proportional valve indicated by a dotted line therein. For example, when the combustion load is 40 [kW], the electric current value of the proportional valve for gas is set to be 88 [mA] that corresponds to the combustion load of 40 [kW] and the rotation rate of the motor 46 is set to be 4,000 [r/min] that corresponds to the electric current value of the proportional valve of 88 [mA]. The relation among the combustion load, the electric current value of the proportional valve, and the rotation rate of the motor 46 depicted in FIG. 18 is prepared in advance by collecting the electric current value of the proportional valve for gas corresponding to the combustion load and the rotation rate of the motor 46 of the air supply fan 44 to establish a predetermined air ratio. On the basis of the relation among the combustion load, the electric current value of the proportional valve, and the rotation rate of the motor, for example, a relation table showing the relation among the combustion load, the electric current value of the proportional valve, and the rotation rate of the motor is produced.

FIG. 19 depicts an example of hardware of the combustion apparatus 20 for the adjustment of the air ratio. A memory part 74 included in the combustion apparatus 20 stores therein the described relation table. The memory part 74 is an example of the storing part that stores therein data, and includes a storing device, such as a flash memory or an electrically erasable and programmable read only memory (EEPROM). A control part 76 included in the combustion apparatus 20 reads the table stored in the memory part 74, adjusts the degree of opening of the proportional valve for gas 78 included in the combustion apparatus 20 to adjust the supply amount of the fuel gas, and adjusts the rotation rate of the motor 46 of the air supply fan 44 to adjust the supply amount of air. The control part 76 adjusts and maintains the air ratios of the air-fuel mixtures based on the relation table. The memory part 74, the control part 76, the motor 46 of the air supply fan 44, and the proportional valve for gas 78 are connected to each other by a connecting line 80.

The relation table may be set regardless of, for example, the combustion stages based on the switching of the combustion area, such as entire combustion, half combustion, or the like of the burner, or may be set for each combustion stage.

The combustion velocity is reduced when the air ratio being equal to or higher than 1 is increased, while the combustion velocity is increased when the air ratio being higher than 1 approaches 1. Variation of the air ratio and variation of the combustion velocity are therefore related with each other. Any waste of the fuel gas is prevented and, in addition, CO and NOx become hard to be generated by adjusting the air ratio corresponding to the magnitude of the combustion amount. For the combustion apparatus 20, the air ratios are adjusted for the combustion to tend to be stable.

(10) It is described in the above embodiment that the air ratio of the main air-fuel mixture f1 is higher than the air ratio of the auxiliary air-fuel mixture f2, that is, the main air-fuel mixture f1 is more air-rich state than the auxiliary air-fuel mixture f2, while the air ratios are not limited to this. The value of the air ratio of the auxiliary air-fuel mixture f2 may be higher than that of the main air-fuel mixture f1.

Aspects of the burner, the combustion apparatus, and the combustion method extracted from the described embodiments are as follows.

An aspect of the burner includes a plurality of burner ports that produce flames using a first air-fuel mixture; and a plurality of auxiliary burner ports that are disposed in a circumference of the burner ports, the plurality of the auxiliary burner ports producing an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture. The air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than 1.

In the burner, the auxiliary flame produced by the plurality of the auxiliary burner ports may be unified to surround the flames, and the auxiliary flame may combust at a position lower than a combustion position of the flames to hold the flames

In the burner, a flow velocity of the first air-fuel mixture may be higher than a flow velocity of the second air-fuel mixture.

In the burner, a gas flow ratio of the first air-fuel mixture supplied to the burner ports to the second air-fuel mixture supplied to the auxiliary burner ports may be set to be at a ratio of 80 to 20 or a ratio in vicinity thereof.

In the burner, air of an amount calculated based on a supplied gas amount or the gas flow ratio may be supplied to the auxiliary burner ports for a set air-fuel mixture amount.

An aspect of the combustion apparatus includes a plurality of burner units. The plurality of the burner units each include a plurality of burner ports that produce flames using a first air-fuel mixture; and a plurality of auxiliary burner ports that are disposed in a circumference of the burner ports, the plurality of the auxiliary burner ports producing an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture. The air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than 1.

An aspect of the combustion method includes producing flames at a plurality of burner ports using a first air-fuel mixture whose an air ratio is higher than 1; and producing an auxiliary flame at a plurality of auxiliary burner ports disposed in a circumference of the burner ports using a second air-fuel mixture whose an air ratio is higher than 1, the air ratio of the second air-fuel mixture being different from the air ratio of the first air-fuel mixture.

Effect of the burner, the combustion apparatus, and the combustion method are listed as follows.

(1) The flame holding function can be enhanced and stabilization of the flame can be facilitated by surrounding the circumference of one burner port by other burner ports.

(2) The flame can be stabilized by the flame holding and reduction of NOx and reduction of CO in the combustion exhaust can be facilitated, by generating the plural air-fuel mixtures whose air ratios are different from each other and whose air ratios are higher than 1.

(3) Occurrence of any flashback can be suppressed by not reducing the flow velocity of the air-fuel mixture against the variation of the supply gas amount.

As above, the most preferred embodiment and the like of the present invention have been described while the present invention is not limited by the above description. It is obvious that those skilled in the art can make various deformations and changes thereto based on the gist of the invention described in claims or disclosed herein. Not to mention, those deformations and changes are included in the scope of the present invention.

According to the burner, the combustion apparatus, and the combustion method that each are an example of the present invention, the flame holding function by the burner can be enhanced, highly stable combustion can be acquired, and air-excessive air-fuel mixtures can be combusted. Advantages can therefore be acquired such as reduction of the exhaust amounts of nitrogen oxides. 

What is claimed is:
 1. A burner comprising: a plurality of burner ports that produce flames using a first air-fuel mixture; and a plurality of auxiliary burner ports that are disposed in a circumference of the burner ports, the plurality of the auxiliary burner ports producing an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture, wherein the air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than
 1. 2. The burner according to claim 1, wherein the auxiliary flame produced by the plurality of the auxiliary burner ports is unified to surround the flames, and the auxiliary flame combusts at a position lower than a combustion position of the flames to hold the flames.
 3. The burner according to claim 1, wherein a flow velocity of the first air-fuel mixture is higher than a flow velocity of the second air-fuel mixture.
 4. The burner according to claim 1, wherein a gas flow ratio of the first air-fuel mixture supplied to the burner ports to the second air-fuel mixture supplied to the auxiliary burner ports is set to be at a ratio of 80 to 20 or a ratio in vicinity thereof.
 5. The burner according to claim 4, wherein air of an amount calculated based on a supplied gas amount or the gas flow ratio is supplied to the auxiliary burner ports for a set air-fuel mixture amount.
 6. A combustion apparatus comprising a plurality of burner units, wherein the plurality of the burner units each comprise: a plurality of burner ports that produce flames using a first air-fuel mixture; and a plurality of auxiliary burner ports that are disposed in a circumference of the burner ports, the plurality of the auxiliary burner ports producing an auxiliary flame using a second air-fuel mixture whose an air ratio is different from an air ratio of the first air-fuel mixture, and wherein the air ratios of the first air-fuel mixture and the second air-fuel mixture are each higher than
 1. 7. A combustion method comprising: producing flames at a plurality of burner ports using a first air-fuel mixture whose an air ratio is higher than 1; and producing an auxiliary flame at a plurality of auxiliary burner ports disposed in a circumference of the burner ports using a second air-fuel mixture whose an air ratio is higher than 1, the air ratio of the second air-fuel mixture being different from the air ratio of the first air-fuel mixture. 